linux-kernel - Re: [PATCH] PCI/ATS: Allow to enable ATS on VFs even if it is not enabled on PF

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Date:   Thu, 16 Feb 2023 09:26:15 +0200
From:   Leon Romanovsky <leon@...nel.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Ganapatrao Kulkarni <gankulkarni@...amperecomputing.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        bhelgaas@...gle.com, jean-philippe@...aro.org,
        darren@...amperecomputing.com, scott@...amperecomputing.com,
        Will Deacon <will@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        Joerg Roedel <joro@...tes.org>,
        linux-arm-kernel@...ts.infradead.org, iommu@...ts.linux.dev
Subject: Re: [PATCH] PCI/ATS:  Allow to enable ATS on VFs even if it is not
 enabled on PF

On Wed, Feb 15, 2023 at 02:57:26PM -0600, Bjorn Helgaas wrote:
> [+cc Will, Robin, Joerg for arm-smmu-v3 page size question]
> 
> On Sun, Feb 12, 2023 at 08:14:48PM +0200, Leon Romanovsky wrote:
> > On Wed, Feb 08, 2023 at 10:43:21AM -0800, Ganapatrao Kulkarni wrote:
> > > As per PCIe specification(section 10.5), If a VF implements an
> > > ATS capability, its associated PF must implement an ATS capability.
> > > The ATS Capabilities in VFs and their associated PFs are permitted to
> > > be enabled independently.
> > > Also, it states that the Smallest Translation Unit (STU) for VFs must be
> > > hardwired to Zero and the associated PF's value applies to VFs STU.
> > > 
> > > The current code allows to enable ATS on VFs only if it is already
> > > enabled on associated PF, which is not necessary as per the specification.
> > > 
> > > It is only required to have valid STU programmed on PF to enable
> > > ATS on VFs. Adding code to write the first VFs STU to a PF's STU
> > > when PFs ATS is not enabled.
> >
> > Can you please add here quotes from the spec and its version? I don't see
> > anything like this in my version of PCIe specification.
> 
> See PCIe r6.0, sec 10.5.1.

Awesome, I have old versions.

Thanks